Left and right front pillars in an automobile are located in a front section of the automobile, and are provided in order to attach a windshield (i.e., a windscreen). Commonly, a front pillar is made as a member having a closed cross section by welding together an outer panel and an inner panel in an overlapping manner. A front pillar of such description is known from Patent Literature 1. Each of the outer panel and the inner panel requires a flange for joining the other. The flange projects outwards from the front pillar. Therefore, the size of the flange increases.
In response, front pillar development has been in progress in recent years. A front pillar using a hollow member integrally formed by hydroforming is known from Patent Literature 2. The front pillar known from Patent Literature 2 comprises the hollow member and an outer panel. The hollow member comprises a pipe formed by hydroforming. The outer panel is provided so as to cover a surface of the hollow member on the outside in the vehicle width direction, and joined. The front pillar known from Patent Literature is smaller than a common front pillar described further above. The visibility range forward of a vehicle body from a passenger compartment (i.e., the visual field) is accordingly larger.
Depending on the model of the automobile, a front pillar may have a curved shape, the entirety of which projects to an outside of a vehicle body, from the viewpoint of design. Even in an instance in which a curved front pillar is used, it is preferable that the pillar exhibits a stiffness equivalent to an instance in which a linear front pillar is used. Increasing the wall thickness or the diameter of the hollow member is one possible method for achieving this. However, there remains the possibility that the weight of the front pillar will increase. There is also a possibility that an increase in the diameter of the hollow member will result in a correspondingly narrower field of view from the passenger compartment.